In the last few years a number of papers have appeared in the research literature which strongly suggest that a cell may regulate the expression of particular genes by methylating certain bases on the DNA molecule (1-5). In addition, it has been shown that protein methylation may play a key role in regulating the activity of proteins (6-8). Both DNA and protein methylation are dependent on any adequate supply of intracellular S- Adenosylmethionine (SAM), the methyl-group donor for the methylation. The objective of this proposed study is to examine the regulation of methylation. The objective of this proposed study is to examine the regulation of S-Adenosylmethionine Synthetase (Methionine Adenosyltransferase) in order to better understand those factors which play critical roles in the synthesis of S-Adenosylmethionine (SAM) and thus the methylation of macromolecules such DNA, RNA, and proteins. The study shall include purification of the enzyme from the yeast and hyphal phase of Mucor racemosus, a search for multiple forms of the enzyme, and characterization of factors which affect the activity and/or synthesis of the enzyme(s).